1. Field of the Invention
The present invention relates to a recording/reproducing apparatus having an optical pickup device, and more particularly, to a recording/reproducing device having an optical pickup device which enables reading out of information from optical disks having different thicknesses and enables recording information thereon.
In the optical pickup of the recording/reproducing device, an objective lens faces a recording surface of an optical disk for focusing light to record information onto the recording surface of the disk or receiving light reflected from the surface of the disk to read information.
2. Description of the Related Art
Recently, research on an optical drive has been conducted in which the drive can seat disks having different thicknesses by adopting a lens device including both a hologram lens and a refractive lens.
FIGS. 1 and 2 show focusing states of a conventional optical pickup device of light incident by zero order diffracted light and 1st order diffracted light on a thin disk and a thick disk, respectively. A refractive lens 2 and a hologram lens 1 are disposed in sequence along an optical path from each of disks 3a and 3b. The hologram lens 1 has a lattice pattern 11 for diffracting light that passes through the hologram lens 1. Thus, while light 4 emitted from a light source (not shown) passes through the hologram lens 1, light is divided into a diffracted 1st order light 41 and a non-diffracted zero order light 40, respectively. While the diffracted 1st order light 41 and the non diffracted zero order light 40 pass through each of the objective lenses 2, the light 41 and 40 are focused with different intensities, thereby forming a focus on the thin disk 3a and on the thick disk 3b. 
The lens device described above can record information on disks having different thicknesses and read out information therefrom using zero order light and 1st order light. However, as the incident light is divided into zero order light and 1st order light, the efficiency of light use is lowered. That is, since the incident light is divided into zero order light and 1st order light by the hologram lens 1, the actual amount of light used for recording information is only 15%. Also, when information is reproduced, information is included in only one of zero order light and 1st order light. Thus, 1st order light or zero order light without information is detected by a photo detector and the detected light may produce noise. The above problem can be overcome by processing the hologram lens of the lens device. However, this requires a high precision process of etching a fine pattern on the hologram, thereby increasing the manufacturing cost.